Editing Fuel cell (section)

=== Solid acid fuel cell ===
{{Main|Solid acid fuel cell}}

Solid acid fuel cells (SAFCs) are characterized by the use of a solid acid material as the electrolyte. At low temperatures, [[solid acid]]s have an ordered molecular structure like most salts. At warmer temperatures (between 140 and 150{{nbsp}}°C for CsHSO<sub>4</sub>), some solid acids undergo a phase transition to become highly disordered "superprotonic" structures, which increases conductivity by several orders of magnitude. The first proof-of-concept SAFCs were developed in 2000 using cesium hydrogen sulfate (CsHSO<sub>4</sub>).<ref>{{Cite journal|last1=Haile|first1=Sossina M.|last2=Boysen|first2=Dane A.|last3=Chisholm|first3=Calum R. I.|last4=Merle|first4=Ryan B.|s2cid=4430178|date=2001-04-19|title=Solid acids as fuel cell electrolytes|journal=Nature| volume=410|issue=6831|pages=910–913|doi=10.1038/35073536|pmid=11309611|issn=0028-0836|bibcode=2001Natur.410..910H|url=https://authors.library.caltech.edu/14197/2/HAInature01supp.pdf |archive-url=https://web.archive.org/web/20170922051627/http://authors.library.caltech.edu/14197/2/HAInature01supp.pdf |archive-date=2017-09-22 |url-status=live}}</ref> Current SAFC systems use cesium dihydrogen phosphate (CsH<sub>2</sub>PO<sub>4</sub>) and have demonstrated lifetimes in the thousands of hours.<ref>{{Cite journal|last1=Haile|first1=Sossina M.|last2=Chisholm|first2=Calum R. I.|last3=Sasaki|first3=Kenji|last4=Boysen|first4=Dane A.|last5=Uda|first5=Tetsuya|date=2006-12-11|title=Solid acid proton conductors: from laboratory curiosities to fuel cell electrolytes|journal=Faraday Discussions| volume=134|doi=10.1039/B604311A|pmid=17326560|issn=1364-5498|pages=17–39|bibcode=2007FaDi..134...17H|url=https://authors.library.caltech.edu/7019/1/HAIfd07.pdf |archive-url=https://web.archive.org/web/20170815181049/http://authors.library.caltech.edu/7019/1/HAIfd07.pdf |archive-date=2017-08-15 |url-status=live}}</ref>